I just disabled this option, and I re-build c::b. I can debug it correctly under GDB(cvs). Maybe, newer gdb don't need such options.
Only tested under WinXP, PCX's GCC 4.6.4, GDB 7.4 (cvs).
I just find that GDB 6.8 (mingw) does not work well on this case. This means if you use GDB 6.8, you should enable this option.